Digital or solid state lighting technologies, i.e., illumination based on semiconductor light sources, such as light-emitting diodes (LEDs), offer a viable alternative to traditional fluorescent, high-intensity discharge (HID), and incandescent lamps. Functional advantages and benefits of LEDs include high energy conversion and optical efficiency, durability, lower operating costs, and many others. Recent advances in LED technology have provided efficient and robust full-spectrum lighting sources that enable a variety of lighting effects in many applications.
Some of the fixtures embodying these sources feature a lighting unit, including one or more LEDs capable of producing white light and/or different colors of light, e.g., red, green and blue, as well as a controller or processor for independently controlling the output of the LEDs in order to generate a variety of colors and color-changing lighting effects, for example, as discussed in detail in U.S. Pat. Nos. 6,016,038 and 6,211,626, incorporated herein by reference. LED technology includes line voltage powered white lighting fixtures, such as the EssentialWhite™, available from Philips Color Kinetics. EssentialWhite™ may be dimmable using trailing edge dimmer technology, such as electric low voltage (ELV) type dimmers for 220 VAC line voltages (or input mains voltages).
Many lighting applications make use of dimmers. Conventional dimmers work well with incandescent (bulb and halogen) lamps. However, problems occur with other types of electronic lamps, including compact fluorescent lamp (CFL), low voltage halogen lamps using electronic transformers and solid state lighting (SSL) lamps, such as LEDs and OLEDs. Low voltage halogen lamps using electronic transformers, in particular, may be dimmed using special dimmers, such as ELV type dimmers or resistive-capacitive (RC) dimmers, which work adequately with loads that have a power factor correction (PFC) circuit at the input.
Conventional dimmers typically chop a portion of each waveform of the input mains voltage signal and pass the remainder of the waveform to the lighting fixture. A leading edge or forward-phase dimmer chops the leading edge of the voltage signal waveform. A trailing edge or reverse-phase dimmer chops the trailing edges of the voltage signal waveforms. Electronic loads, such as LED drivers, typically operate better with trailing edge dimmers. Unlike incandescent and other resistive lighting devices which respond naturally without error to a chopped sine wave produced by a phase chopping dimmer, LEDs and other solid state lighting loads may incur a number of problems when placed on such phase chopping dimmers, such as low end drop out, triac misfiring, minimum load issues, high end flicker, and large steps in light output.
Radio or radio frequency (RF) controlled lighting units generally include onboard radio transceivers or modems, and are often referred to as “connected lamps,” such as the Philips Hue. However connected lamps do not always work well in combination with wall dimmers or electronic switches. Such electronic switches are used, for example, in various sensors that enable automatic operation of the lighting units, including daylight sensors, presence/occupancy detectors, or remotely controlled switches, such as in the ClickOnClickOff (COCO) portfolio, for example. In the future, when multiple control systems need to work together (e.g., radio controlled lamps plus building management systems that switch groups of light sockets), electronic switches may become more common.
Most consumer lighting controllers are two-wire devices. A problem therefore arises when a dimmer or electronic switch interrupts just one of the two wires, as discussed below. In fact, most consumer lighting controllers are two-wire devices that only interrupt the live wire. In this configuration there is no neutral connection to the lighting controller that would enable the off-state current to run through the lighting unit(s). An off-state bleeder may be included to ensure that the lighting unit does not flicker or glow when the dimmer is switched off. In case, however, the RF radio (transceiver or modem) in a conventional radio control lighting device is no longer functional, as a practical matter, when the dimmer or switch is in off-state.
A lighting unit controlled by a two-wire device, for example, works well when the lamp appears as a low impedance load, as in the case of an incandescent lamp. The lamp must provide a current path to keep the dimmer or switch in operation. When the lamp comprises an LED lamp, though, the load may be so high-impedance that even with the very small remaining leakage current through the switch, the lamp can start to emit (some) light and boot software running on its internal microcontroller. This behavior leaks to visible glowing or flickering, and is undesired when the dimmer or electronic switch is set in an off-state.
To prevent this undesirable operation, a conventional LED lamp may include an “off-state bleeder,” which is a small electronic circuit connected in parallel with the LED lamp. The off-state bleeder ensures that there is always enough current floating such that the dimmer or switch may continue to function, and that the LED lamp remains off when the dimmer or electronic switch is in the off-state. This configuration resolves the problem by provide flow of a small current when the electronic switch or lamp is in the off-state.
However, the connected lamp may draw too little power to let this current flow. If the dimmer or electronic switch no longer functions as a result, it may fail to switch on again. Also, the connected lamp sees some power on its mains power line connector, and may try to boot up. The connected lamp may flicker during this attempt, which may be annoying to the user.
Thus, there is a need in the art to detect improper operation of lighting system components, such as the dimmer and/or the solid state lighting load driver, and to identify and implement corrective action to correct the improper operation and/or remove power to the solid state lighting load, to eliminate undesirable effects, such as light flicker.